The inventors of the present application have invented an optical path switching apparatus and a relevant method based on a new principle (see patent literature 1). The invented optical path switching apparatus is configured to irradiate a control light absorbing area of a thermal lens forming element with control light in a wavelength band that can be absorbed by the control light absorbing area and signal light in a wavelength band that cannot be absorbed by the control light absorbing area in such a manner that optical axes of the control light and the signal light coincide with each other when the control light and the signal light converge. According to the above-described configuration, irradiation of the control light can be selectively performed when the control light absorbing area of the thermal lens forming element is irradiated with the signal light. More specifically, in a case where irradiation of the control light and irradiation of the signal light are not simultaneously performed, the signal light passes through a hole of a mirror and travels straight. On the other hand, in a case where irradiation of the control light and irradiation of the signal light are simultaneously performed, the signal light is reflected by the mirror that is inclined relative to the traveling direction of the signal light. In other words, the optical path of the signal light is changed by the mirror. In this respect, the patent literature 1 discloses an optically controlled optical path switching apparatus that can switch the traveling direction of the signal light between two directions using the control light having only one type of wavelength.
Further, the inventors of the present application have invented an optically controlled optical path switching type optical signal transmission apparatus and a relevant optical signal optical path switching method, in which a plurality of thermal lens forming elements are combined with hole-formed mirrors (see patent literature 2). According to the invented optical path switching type optical signal transmission apparatus, a wavelength band that can be absorbed by a control light absorbing area and a wavelength of control light are in a one to one relationship. Further, the invented optical path switching type optical signal transmission apparatus uses a combination of a total of seven thermal lens forming elements, which have three types of control light absorbing areas, for example, pigments used for which are different in absorbing wavelength band. In addition, the invented optical path switching type optical signal transmission apparatus realizes an optically controlled switching system capable of distributing data of a server to eight destinations by ON-OFF controlling the control light having three types of wavelengths.
Further, as disclosed in patent literatures 3 to 6, the inventors of the present application have further proposed another optical path changing methods and optical path switching apparatuses.
According to the proposed optical path changing methods and the optical path switching apparatuses, emission of control light in a wavelength band that can be absorbed by the control light absorbing area and emission of signal light in a wavelength band that cannot be absorbed by the control light absorbing area are performed so as to let both the lights enter into a control light absorbing area of a thermal lens forming optical element and converge in the control light absorbing area. In this case, a light convergence point of the control light is differentiated from a light convergence point of the signal light. Therefore, both the control light and the signal light converge on an incidence plane of the control light absorbing area or its vicinity in the light traveling direction, and then diffuse respectively. As a result, in the control light absorbing area, the temperature increases locally in the area where the control light is absorbed and its peripheral area. According to the above-described increase in temperature, the structure of the thermal lens changes reversibly. The refractive index substantially changes, and the traveling direction of the signal light changes correspondingly.
Each of the patent literatures 4 and 5 discloses a one-to-two compatible optically controlled optical path switching apparatus that can switch the traveling direction of control light to one of two directions using control light having a single wavelength. Further, the patent literature 6 discloses an optically controlled optical path switching apparatus that can switch the optical path of signal light to be emitted from a central fiber of an end face closely-arranged seven-core optical fiber to one of, for example, seven directions, using control light that can be emitted from six optical fibers provided around the central fiber. In the following description, the optically controlled optical path switching apparatus discussed in the patent literature 6 is referred to as “one-to-seven compatible optically controlled optical path switching apparatus.” Further, patent literature 7 discloses an end face closely-arranged multi-core optical fiber and its manufacturing method, which can be used for the one-to-seven compatible optically controlled optical path switching apparatus.
Patent literature 8 discloses, in FIG. 5, a “reflection-type star coupler” that includes a plurality of optical fibers or optical waveguides bound together to form an integrated optical path of the optical fibers or the integrated optical waveguide and a total reflection mirror provided at an end face of the integrated optical path. The above-described reflection-type star coupler can be used to constitute a “reflection-type star coupler based optical LAN” that can receive an optical signal transmitted from an optical transmission/reception apparatus, which is connected to respective optical fibers or optical waveguides, and can uniformly distribute the optical signal to a plurality of optical transmission/reception apparatuses. However, according to the above-described optical LAN, it is necessary to additionally use a time division multiplexing or wavelength division multiplexing control technique to prevent any collision between optical signals transmitted from a plurality of optical transmission/reception apparatuses.
In view of the widespread use of the Internet conformable to the communication standard “TCP/IP protocol” and the necessity of handling massive communication data, and further as a prospective communication means replaceable with the old-fashioned current telephone circuit network, there is a recent movement, so-called “Fiber To The Home (FTTH)”, which introduces optical fibers to general houses. To this end, optical fiber networks that are adapted to wavelength multiplex optical communication specifications are widely built and operated in individual houses for the FTTH. Utilization of the FTTH system is useful to promote an advanced communication environment, i.e., so-called “triple play”, which can provide three types of services “Internet communications”, “IP packet telephones”, and “audio/visual (AV) distributions.” In this case, a wavelength division multiplexing optical communication technique is practically employable to transmit three types of optical communication signals via one optical fiber. More specifically, as illustrated in FIG. 8, various signal lights are presently used for “Internet communications” and “IP packet telephones.” The signal light to be used for an “uplink optical signal” transmitted from each user side device to a station building apparatus is signal light in a wavelength range from 1260 nm to 1360 nm (having a central wavelength of 1310 nm). The signal light to be used for a “downlink optical signal” transmitted from the station building apparatus to each user side device is signal light in a wavelength range from 1480 nm to 1500 nm (having a central wavelength of 1490 nm). Further, the signal light to be used for distribution of AV signals from the station building apparatus to each user side device is signal light having a wavelength of 1550 nm.                Patent Literature 1: JP 3809908 B        Patent Literature 2: JP 3972066 B        Patent Literature 3: JP 2007-225825 A        Patent Literature 4: JP 2007-225826 A        Patent Literature 5: JP 2007-225827 A        Patent Literature 6: JP 2008-083095 A        Patent Literature 7: JP 2008-076685 A        Patent Literature 8: JP 2000-121865 A        